Installation switching devices of this generic type, for example motor protection switches, have at least one pole current path, comprising two stationary contact pieces and two moving contact pieces which are arranged on a moving contact bridge and form a double-break pole switch with two contacts.
In this case, a pusher acts on the contact bridge in the opening direction, and a contact compression spring acts on it in the closing direction.
Furthermore, installation switching devices of this generic type have an electromagnetic release whose armature not only acts on the contact bridge via the pusher in the opening direction but also unlatches the latching point of a switch latch when a short-circuit current occurs in the pole current path, as a result of which the switch latch permanently acts on the contact bridge in the opening sense, against the force of the contact compression spring, via an operating lever.
Immediately after the striking on the contact bridge and thus the breaking of the short-circuit current in the pole current path, the electrodynamic recoil of the electromagnetic release collapses, and the force of the contact compression spring once again acts on the contact bridge in the direction of its closed position.
As a result of the greater mechanical inertia of the switch latch, compared with that of the system comprising the armature and the pusher, the operating lever lags behind the pusher movement in order to hold the contacts permanently open by means of the switch latch.
In unfavorable conditions, it is possible for the contacts to have already been closed again by the contact compression spring before the switch latch can provide permanent opening via the operating lever and the pusher. This is then referred to as contact bouncing, which is undesirable.